.AM S3 



INITED STATES DEPARTMENT OF AGRICl 

BULLETIN No. 881 




Contribution from the Bureau of Plant Industry • * _ 

J\^^^U WM. A. TAYLOR, Chief iCT^SOL 




Washington, D. C. T August 10, 1920 

EFFECT OF ALFALFA ON THE SUBSEQUENT YIELDS 
OF IRRIGATED FIELD CROPS. 

By C. S. Scofield, 
Agriculturist in Charge, Office of Western Irrigation Agriculture. 



CONTENTS. 

Page. 



Aim of the experiments 1 

Description of the experiments 2 

Results of the experiments 3 

Irish potatoes 3 



Results of the experiments— Continued. 

Oats 7 

Sugar beets 9 

Summary 12 



AIM OF THE EXPERIMENTS. 

It has long been recognized that the growing of alfalfa has a 
beneficial effect upon the producing capacity of irrigated lands; in 
other words, crops grown on land following alfalfa give larger yields 
than those following nonleguminous crops. In the series of experi- 
ments here reported it is aimed to show the extent of this beneficial 
effect as observed with three common field crops in several different 
rotations at three different locations in the northern Great Plains. 

These experiments were conducted by the Bureau of Plant Industry 
at the following places: (1) The Scottsbluff Field Station, 1 located 
on the North Platte Reclamation Project, near Mitchell, Nebr.; 
(2) the Belle Fourche Field Station, located on the Belle Fourche 
Reclamation Project, near Newell, S. Dak.; and (3) the Huntley 
Field Station, 2 located on the Huntley Reclamation Project, near 
Huntley, Mont. These stations are so situated as to be representa- 
tive of conditions on much of the irrigated land in the northern 
Great Plains, and it is believed that the results secured are generally 
applicable to that region. 3 

1 The work of this field station is conducted and supported cooperatively by the United Btates Depart- 
ment of Agriculture and the Nebraska Agricultural Experiment Station. 

' The work of this field station is conducted and supported cooperatively by the United Btates Depart- 
ment of Agriculture and the Montana Agricultural Experiment Station. 

8 For a brief description of the agricultural and soil conditions of this region, see Scofield, C. S., Effect 
of farm manure in stimulating the yields of irrigated field crops. In Jour. Agr. Research, v. 15, No. 9, 
pp. 493-503. 1918. 

185530°— 20— Bull. 881 






2 BULLETIN 881, TJ. S. DEPARTMENT OF AGRICULTURE. --^/^ C~> 

DESCRIPTION OF THE EXPERIMENTS. 

These experiments are a part of an extensive series of rotations 
conducted under irrigation at the three stations specified. The 
experiments were started with the crop season of 1912 and have been 
continued without modification. The field plats, which include one- 
fourth of an acre each, are laid out in series. The series are separated 
by 40-foot roads, and the plats in the series are separated by 5-foot 
alleys. The plats at Scottsbluff are 132 feet long by 82.5 feet wide; 
those at Belle Fourche are 264 feet long by 41.25 feet wide, and 
those at Huntley are 227 feet long by 48 feet wide. 

The present bulletin deals with the effect produced by growing 
alfalfa for one, two, or three years on plats which are later used for 
two or three years for other crops and then are reseeded to alfalfa. 
The alfalfa crops are cut for hay, and at the end of the alfalfa period 
the land is plowed soon after the last cutting, so that only the stubble 
is plowed under. The results are based on seven pairs of rotations, 
the two members of each pair differing from each other only in that 
one member includes either two years or three years of alfalfa, while 
the other does not. Each rotation occupies as many plats as there 
are years in the cycle, so that each crop is represented each year. 
The crops and sequences involved in the 14 rotations are as follows: 

Rotation 20: Potatoes, sugar beets. 

Rotation 40: Alfalfa, alfalfa, potatoes, sugar beets. 

Rotation 22: Oats, sugar beets. 

Rotation 42: Alfalfa, alfalfa, oats, sugar beets. 

Rotation 24: Potatoes, oats. 

Rotation 44: Alfalfa, alfalfa, potatoes, oats. 

Rotation 28: Wheat, oats. 

Rotation 48: Alfalfa, alfalfa, wheat, oats. 

Rotation 30: Potatoes, oats, sugar beets. 

Rotation 60: Alfalfa, alfalfa, alfalfa, potatoes, oats, sugar beets. 

Rotation 31: Potatoes, oats, sugar beets (manured). 

Rotation 61: Alfalfa, alfalfa, alfalfa, potatoes, oats, sugar beets (manured). 

Rotation 32: Corn, oats, sugar beets. 

Rotation 62: Alfalfa, alfalfa, alfalfa, corn, oats, sugar beets. 

It will be noted from the list of rotations that the comparisons 
to determine the effect of the alfalfa are made between 2-year and 
4-year rotations and between 3-year and 6-year rotations. In the 
first set of comparisons a 2-year period of alfalfa is used and in the 
second set a 3-year period. 

As these rotation experiments were started in 1912, in each case 
on land that had not previously grown alfalfa, there was no effect to 
be observed until 1913, and the crops grown that year following alfalfa 
were from plats that had been in alfalfa only one season. The first 
full effect of the alfalfa in the rotation was obtained in the 4-year 
rotations in 1914 and in the 6-year rotations in 1915, and then only 
in the case of crops which immediately succeed alf alf a in the rotation. 



EFFECT OF ALFALFA ON YIELDS OF FIELD CROPS. 3 

In the above list of the seven rotations which include alfalfa, 
that crop was followed by potatoes in four cases and by oats, wheat, 
and corn in the other three. The second-year effect of alfalfa is 
shown in two cases on sugar beets and in five cases on oats. In 
the three 6-year rotations, sugar beets are grown the third year fol- 
lowing the alfalfa and presumably, therefore, derive the least benefit 
from that crop. 

The cultural operations used with these rotations have been only 
those demanded by good farming. With respect to any one crop, 
the same variety has been used in all rotations at each station each 
year. The same varieties have not been used at the different stations, 
nor has the same variety been used for all years at the same station. 
It has been the aim to use one of the best of the locally adapted 
varieties in each case. 

In the rotations where alfalfa follows sugar beets, the alfalfa has 
been seeded in the spring following the beet crop, and consequently 
it has done little more than get well established the first year. Where 
the alfalfa follows oats it has been customary to seed it in the fall 
in the oat stubble, and in general this has resulted in a good stand 
and nearly a full crop the following season. At the close of the alfalfa 
period in these rotations the alfalfa sod has been plowed immediately 
after the last cutting. This first plowing or "crowning," as it is 
called, is done only 3 or 4 inches deep, in order to cut the roots 
close to the surface and kill the plants. After the inverted sod has 
dried out well it is disked, and the land is then plowed to a depth of 
8 or 9 inches. 

The field work of these rotation experiments has been under the 
direction of the farm superintendent at each station and under the 
immediate supervision of a scientific assistant, who is charged with 
performing or directing the cultural operations, the irrigation, and 
the harvesting, and with taking the field notes and reporting the 
results each year. 1 

RESULTS OF THE EXPERIMENTS. 

IRISH POTATOES. 

There are four pairs of rotations at each station in which the mem- 
bers of the pairs differ from each other only in that one includes a 
period of alfalfa and the other does not. In two of these cases, 

1 The following is the personnel concerned with the field work of these rotation experiments: At Scotts- 
bluff, Mr. Fritz Knorr wassuperintendentfroml910totheendofl916. Mr. JamesA. Holden was in charge 
of the irrigated rotations from the spring of 1912 until the end of 1910, when he succeeded Mr. Knorr as 
farm superintendent. Mr. David W. Jones supervised the irrigated rotation work during 1917 and the 
early part of 1918, when he entered the military service; during the remainder of the season Mr. Holden 
directed the work. At Belle Fourche, Mr. Beyer Aune has been superintendent since 1909. He has kept 
in close touch with the irrigated rotation work, being assisted at different times by Mr. John is. Wantz, 
Mr. X. L. Mattice, Mr. George T. Ratliffe, and Mr. Oscar Ii. Mathews. At Huntley Mr. Dan Hansen 
has been superintendent since 1910. The irrigated rotations were under the supervision of Mr. John M. 
Spain during 1912, Mr. John W. Knorr dining 1914, and Mr. Edward G.Noble from 1915 until the summer of 
1918, when Mr. Xobleentered the military service. Mr. Hansen directed the work in 1913 and during the 
latter part of 1918. 



4 BULLETIN" 881, U. S. DEPARTMENT OF AGRICULTURE. 

rotations 40 and 44, the alfalfa period covers two years and in rota- 
tions 60 and 61 it covers three years. In the above-enumerated 
rotations the 1913 potato crops followed only one year of alfalfa. 
In 1914 they followed two years of alfalfa, which is the normal course 
for the first two rotations, 40 and 44, while for rotations 60 and 61 
the normal course of three years of alfalfa was first reached for the 
crop of 1915. 

Table I shows the yields of potatoes for the four pairs of rotations 
at each of the three stations. These yields, given in bushels per acre, 
are for the total crop, including small and diseased potatoes. The 
annual difference in yield between the crops following alfalfa and 
the check plats are also shown in the table, together with the mean 
annual yield of the crop for each rotation and the mean of the 
annual differences in yield. With each of the means the probable 
error is given. 1 

The results given in Table I show that in nine cases out of twelve 
the mean of the annual differences in yield was in favor of the crops 
following alfalfa. But in only six of the nine cases is this mean 
difference significant; that is, more than three times the probable 
error. In the other six cases the mean is less than three times the 
probable error and is not regarded as significant. 

It has been customary in connection with these experiments to 
sort the potatoes in the field at the time of digging. This sorting 
has been done by means of a wire screen with 2-inch meshes. The 
smaller potatoes that pass through this screen are classed as un- 
marketable, while those passing over the screen are marketable. 
It has been observed that at Scottsbluff the percentage of marketable 
potatoes has been significantly larger from the plats following alfalfa 
than from the check plats. This has not been true, however, at 
Belle Fourche or at Huntley. 

It is clear from the facts set forth in Table I that the beneficial 
effect of alfalfa on subsequent yields of potatoes has been much more 
marked and consistent at Scottsbluff than at the other two stations. 
This may be due to the fact that the soil at Scottsbluff is a light sandy 
loam, while at both the other stations the soil is a heavy clay loam. 
The essential facts concerning these yields for each of the three sta- 
tions are summarized in the following paragraphs. 

At Scottsbluff the yield of potatoes, large and small, for the 48 
plat years has averaged 236 bushels per acre, with a mean annual 
difference resulting from alfalfa of 100 ± 7. The yield of marketable 

1 The probable error of the mean as used in these tables is obtained by Merriman's formula 36, which is 

A QA CO -j 

stated as follows: r o p=» ■ ' In other words, the probable error of the mean is obtained by multiply- 

nyra— 1 
Ing the sum of the departure frsm the mean by the quotient oin-^n—l into 0.4853, where n equals the 
number of yields involved. (Merriman, Mansfield. Method of Least Squares, ed. 8, p. 223. New York, 
London, 1913.) 



EFFECT OF ALFALFA ON YIELDS OF FIELD CROPS. 



potatoes from the same plats excepting 1918, when this classification 
was not made, has averaged 192 bushels per acre, with a mean 
annual difference in favor of those following alfalfa of 101 ± 7. Again 
omitting the crop of 1918, the percentage of the total yield classed 
as marketable is 76, while the mean annual difference in percentage 
marketable in favor of those following alfalfa is 12 ±1.3. 

Table I. — Effect of alfalfa on the yields of Irish potatoes at the Scottsbhiff, Belle Fourche, 
and Huntley Field Stations, for the 6-year period from 1913 to 1918, inclusive. 



Station and rotation No. 


Yield of potatoes per acre (bushels). 


1913 


1914 


1915 


1916 


1917 


1918 


Mean. 


Scottsbluff: 

20 (no alfalfa) 


398 
403 


146 
280 


88 
206 


142 
285 


131 
273 


87 
179 


165 ±29 




271 + 20 






Difference 


+ 5 


+ 134 


+ 118 


+ 143 


+ 142 


+ 92 


+ 106+14 






24 (no alfalfa) 


235 
402 


146 
319 


109 
228 


217 
308 


134 
290 


150 
-227 


165+15 




296+18 








+ 167 


+ 173 


+ 119 


+ 91 


+ 156 


+ 77 


+ 131 ±13 






30 (no alfalfa) 


329 
322 


216 
272 


146 
231 


226 
319 


167 
281 


79 
238 


194±24 


60 (following alfalfa) 


277±11 






Difference 


- 7 


+ 56 


+ 85 


+ 93 


+ 114 


+ 159 


+ 83 + 15 






31 (no alfalfa^ 


353 
380 


243 
299 


175 
220 


244 
306 


211 
346 


81 
249 


218 + 23 




300+17 






Difference 


+ 27 


+ 56 


+ 45 


+ 62 


+ 135 


+ 168 


+ 82±17 






Belle Fourche: 

20 (no alfalfa) 


128 
88 


86 
96 


102 
94 


157 
129 


133 
124 


167 
203 


129+ 9 


40 (following alfalfa) 


122+11 






Difference 


- 40 


+ 10 


— 8 


- 2S 


- 9 


+ 36 


- 7+ 7 






24 (no alfalfa) 


109 
177 


112 
127 


111 
144 


151 
149 


120 
170 


191 
153 


132 ±10 


44 (following alfalfa) 


153± 5 






Difference 


+ 68 


+ 15 


+ 33 


- 2 


+ 50 


- 38 


+ 21+11 






30 (no alfalfa) 


74 

97 


68 
105 


59 
105 


166 
119 


139 
108 


168 
170 


112+17 


60 (following alfalfa) 


117+ 7 






Difference 


+ 23 


+ 37 


+ 46 


- 47 


- 31 


+ 2 


+ 5+11 






31 (no alfalfa) 


90 
139 


140 
112 


137 
115 


188 
124 


205 
130 


231 
165 


165 ±'16 


61 (following alfalfa) 


131+ 5 






Difference 


+ 49 


- 28 


- 22 


- 64 


- 75 


- 66 


- 34+13 






Huntlev: 

20 (no alfalfa) 


200 

250 


179 
156 


350 
350 


228 

247 


241 

224 


390 

415 


265 ±20 


40 (following alfalfa) 


279 ±30 






Difference 


+ 50 


- 23 





+ 19 


- 17 


+ 55 


+ 14+10 






24 (no alfalfa) 


316 
113 


171 
195 


273 
190 


236 
166 


229 
182 


315 

373 


257±17 




203 ±21 








-203 


+ 24 


- 83 


-70 


-47 


+ 58 


- 54±25 






30 (no alfalfa) 


188 
285 


156 
293 


22S 
397 


224 
292 


175 

23 S 


286 

345 


209±14 


60 (following alfalfa) 


308± 16 






Difference 


+ 97 


+ 137 


+ 169 


+ 68 


+ 63 


+ 59 


+ 99 ±14 






31 (no alfalfa) 


160 

277 


140 
184 


273 
420 


212 

in.' 


91 

2117 


324 

471 


200 ±26 


61 (following alfalfa) 


343±34 






Difference 


+ 117 


+ 44 


+ 147 


+ 190 


+ 206 


+ 150 


+ 143+15.5 







6 BULLETIN 881, IT. S. DEPARTMENT OF AGRICULTURE. 

At Belle Fourche the yield of potatoes, large and small, for the 48 
plat years has averaged 135 bushels per acre, while the mean annual 
difference resulting from the growing of alfalfa has been a decrease 
of 4 ± 6. The yield of marketable potatoes from the same plats has 
averaged 107 bushels per acre, with a mean annual decrease for the 
plats following alfalfa of 4 ±5.6. The percentage of the total yield 
classed as marketable for the 48 plats is 81, with a mean annual 
difference in favor of the plats following alfalfa of 0.5 ±2.2. These 
results indicate that at Belle Fourche there has not been, so far, any 
beneficial effect from alfalfa on subsequent yields of potatoes. 

At Huntley the total yield of potatoes for the 48 plat years has 
averaged 258 bushels per acre, while the mean annual difference in 
favor of the plats following alfalfa is 50 ± 12.6. The yield of market- 
able potatoes from the same plats has averaged 241 bushels per acre, 
with a mean annual difference in favor of the plats following alfalfa of 
55 ±11.4. The percentage of the total crop classed as marketable 
is 93, with the difference in favor of the plats following alfalfa of 
1±0.55. Thus, the results from the Huntley station indicate that 
the beneficial effect of alfalfa on subsequent potato crops, though 
fairly large, is, when judged by the size of the probable error, barely 
significant. 

In an earlier paper, the effects of farm manure on the crop yields 
in certain of these irrigated rotations was reported, 1 and it seems 
proper to present here a comparison between the effects of periodical 
applications of farm manure and the use of alfalfa in the rotation. 
Such a comparison of results appears to be justified, because the 
two tests were made in the same fields and the same set of plats were 
used as checks in both cases. The experiments reported for the 
test of farm manure covered the 6-year period from 1912 to 1917, 
while those of alfalfa covered the 6-year period from 1913 to 1918. 
There were, however, only three rotation pairs for the potato ex- 
periments with manure, while there were four pairs with alfalfa. 
Also, in the manure experiments the manure was applied immedi- 
ately preceding the potato crop in two of the three cases and to the 
sugar-beet crop, which preceded the potatoes, in the third case. In 
the alfalfa experiments the potato crop followed the alfalfa in all 
four cases. 

The comparative features of the two experiments are summarized 
in Table II. 

The results brought together in Table II show clearly that on the 
lighter soil of the Scottsbluff station both manure and alfalfa have a 
beneficial effect on the yield of potatoes. The manure has resulted 
in an increased total yield of the treated plats over that of the check 

1 Scofield, C. S. Loc. cit. 



EFFECT OF ALFALFA ON" YIELDS OF FIELD CROPS. 



plats of 40 bushels per acre, while the alfalfa has increased the yield 
by 100 bushels per acre over that of the check plats. At Belle 
Fourche and at Huntley the beneficial effects of manure have been 
at least significant. The alfalfa has not produced increased yields 
at Belle Fourche, though it has done so at Huntley. 

Table II. — Comparison of the effect of farm manure and of alfalfa on subsequent yields 
of Irish potatoes in crop rotations under irrigation at the Scottsbluff, Belle Fourche, 
and Huntley Field Stations. 



Factors compared. 



Yield of potatoes per acre. 



Scottsbluff. 



Manure. Alfalfa 



Belle Fourche. 



Manure. Alfalfa 



Huntley. 



Manure. Alfalfa 



Total crop: 

Yield (mean of check and treated 
plats) bushels. 

Mean annual difference do. . . 

Marketable potatoes: 

Yield do. . . 

Mean annual difference in yield. do. . . 

Percentage 

Mean annual difference in percentage. 



208 

40±7 

150 

40 ±7 

72 

8±1.5 



236 
100±7 

192 

101 ±7 

76 

12±1.3 



131 

34±6.4 



105 
36±6.3 



7±1.9 



135 
-4±6 

107 

-4±5.6 

81 

.5±2.2 



239 
26±8.3 

221 

24±8.5 
92 



258 
50±12.6 

241 

55±11.4 

93 

1±.55 



OATS. 



The effect of alfalfa on the subsequent yield of oats is shown in 
Table III for six pairs of rotations at Scottsbluff and Belle Fourche 
and for four pairs at Huntley. The oats crop follows directly after 
alfalfa in only one rotation (No. 42) at each station. In all the other 
rotations the oats occur as the second crop after alfalfa, being preced- 
ed by potatoes in three cases (Nos. 44, 60, and 61), by wheat in one 
case (No. 48), and by corn. in one (No. 62). Because of this position 
in the rotation the oats did not come on plats that had been in alfalfa 
until 1914 except in the case of rotation No. 42. Thus, 16 compari- 
sons are made in Table III, of which 12 show increases in the mean 
yield of the crops following alfalfa and 4 show decreases. But if 
we accept as a test of significance of the mean that it shall be at 
least three times as large as its probable error, then only 5 of the 16 
comparisons show definite benefits from the alfalfa, and in one case, 
(rotation No. 42, at Belle Fourche) there is a consistent reduction 
in yield following alfalfa. 

While these results do not show a strikingly beneficial effect from 
the use of alfalfa in the rotation, it is to be observed that these oat 
crops have been grown on soil that was virgin at the beginning of tho 
experiment and of relatively high productivity, as shown by the 
mean yields of all the plats included in the experiment. It has been 
noted also in connection with these experiments that the plant 
growth has been more vigorous on the plats of oats following alfalfa, 
as is shown in the yields of straw. These notes, together with the 
facts concerning the grain yields for each of the three stations, are 
summarized below. 



BULLETIN 881, U. S. DEPARTMENT OF AGRICULTURE. 



Table III. — Effect of alfalfa on the 
Huntley Field Stations during 



yields of oats at the Scottsbluff, Belle Fourche, and 
the 6-year period from 1913 to 1918, inclusive. 



Station and rotation No. 


Yield of oats per acre (bushels). 


1913 


1914 


1915 


1916 


1917 


1918 


Means. 


Scottsbluff: 

22 (no alfalfa) 


90 
101 


76 
95 


16 
16 


49 
55 


75 
79 


53 
71 


60±8 




70±8 








+ 11 


+ 19 





+ 6 


+ 4 


+ 18 


+ 10+2 






24 (no alfalfa) 




69 
95 


19 
20 


56 
62 


65 
69 


50 

72 


52±G 






64±G 












+ 26 


+ 1 


+ 6 


+ 4 


+ 22 


+ 12 + 4 








28 (no alfalfa) 




65 
83 


9 

22 


33 
41 


53 

61 


44 
59 


41 + 7 






53 + 7 












+ 18 


+ 13 


+ 8 


+ 8 


+ 15 


+ 12±1.5 








30 (no alfalfa) 




79 

84 


16 

18 


64 
56 


65 

74 


69 

77 


59±7 






62±S 












+ 5 


+ 2 


- 8 


+ 9 


+ 8 


+ 3±2 








31 (no alfalfa) 




86 
83 


20 
19 


71 

56 


88 
76 


80 
90 


69 + 8 






65±9 












- 3 


- 1 


- 15 


- 12 


+ 10 


- 4±3 








32 (no alfalfa) 




51 
70 


10 
12 


68 
48 


61 
65 


60 
79 


50±7 






55±S 












+ 19 


+ 2 


- 20 


+ 4 


+ 19 


+ 5 + 5 








Belle Fourche: 

22 (no alfalfa) 


45 
26 


77 
61 


99 
75 


57 
36 


71 
35 


87 
48 


73±6 




47±5 








- 19 


- 16 


- 24 


- 21 


- 36 


- 39 


-26 + 3 






21 (no alfalfa) 




74 
110 


112 
116 


58 
58 


73 

72 


90 
83 


81±7 






88±9 












+ 36 


+ 4 





- 1 


- 7 


+ 7±5 








28 (no alfalfa) 




26 

105 


50 

118 


27 
58 


40 
69 


36 

86 


36±3 


48 (following alfalfa) 2 years 




87 + 7 












+ 79 


+ 68 


+ 31 


+ 29 


+ 50 


+ 51 + 7 








30 (no alfalfa) 




93 
95 


107 
109 


56 
50 


66 
52 


70 
78 


78+7 


60 (following alfalfa) 2 years 




77±9 












+ 2 


+ 2 


- 6 


- 14 


+ 8 


— 1±3 








31 (no alfalfa) 




90 
100 


104 
114 


71 

83 


76 
49 


81 

81 


84±4 






85 ±7 












+ 10 


+ 10 


+ 12 


- 27 





+ 1±5 












92 
104 


68 
80 


62 
64 


41 

45 


54 
67 


64 + 6 


62 (following alfalfa) 2 years 




72±7 








Difference 




+ 12 


+ 12 


+ 2 


+ 4 


+ 13 


+ 8±2 








Huntley: 

22 (ho alfalfa) 


97 
103 


109 

84 


79 
73 


94 

91 


81 
89 


99 
103 


93±3 


42 (following alfalfa) 1 year 


90±3 






Difference 


+ 6 


- 25 


- 6 


- 3 


+ 8 


+ 4 


- 3±3 






24 (no alfalfa) 




103 
105 


81 

77 


72 
83 


68 
62 


93 
93 


83±5 


44 (following alfalfa) 2 years 




84±5 








Difference 




+ 2 


- 4 


+ 11 


- 6 





+ 1 + 2 








30 (no alfalfa) 




87 
108 


104 

82 


47 
102 


46 
87 


80 
127 


73 + 9 


60 (following alfalfa) 2 years 




101 ±6 








Difference 




+ 21 


- 22 


+ 55 


+ 41 


+ 47 


+28±10 








31 (no alfalfa) 




94 
103 


103 
76 


T 
105 


50 
111 


86 
119 


82±6 


61 (following alfalfa) 2 years 




103 ±4 








Difference 




+ 9 


- 27 


+ 28 


+ 61 


+ 33 


+21 ±10 









EFFECT OF ALFALFA ON" YIELDS OF FIELD CROPS. 9 

At Scottsbluff the yield of oats, grain, for the 62 plat years has 
averaged 58 bushels per acre, with a mean annual difference in favor 
of those following alfalfa of 6 ±1.3. The yield of straw from these 
same plats, omitting the crop of 1915, which was injured by hail 
and cut with a mower, has averaged 1.28 tons per acre, with a mean 
annual difference in favor of the plats following alfalfa of 0.30 ±0.05. 
Thus, while the yield of grain following alfalfa was increased by 10 
per cent of the mean yield of all plats, the yield of straw was increased 
by 23 per cent. 

At Belle Fourche the yield of grain for the 62 plat years has aver- 
aged 72 bushels per acre, with a mean annual difference in favor of 
those following alfalfa of 5 ± 3 . The yield of straw from these same 
plats has averaged 1.24 tons per acre, with a mean annual difference 
in favor of the plats following alfalfa of 0.31 ±0.06. Thus, the yield 
of grain following alfalfa has been increased by 7 per cent, while the 
yield of straw has been increased 25 per cent. 

At Huntley the yield of grain for the 42 plat years has averaged 88 
bushels per acre, with a mean annual difference in favor of the plats 
following alfalfa of 11 ±3.7. The yield of straw from these same 
plats has averaged 1.51 tons per acre, with a mean annual difference 
in favor of the plats following alfalfa of 0.55 ±0.05. Thus, while the 
increase in the yield of grain has been 12.5 per cent, the increase in the 
yield of straw has been 36 per cent. 

SUGAR BEETS. 

The effect of alfalfa on the yield of sugar beets is shown in Table IV. 
Five pairs of rotations are reported for Scottsbluff and Belle Fourche 
and four pairs for Huntley. Two of the rotations at each station 
cover four years, the sugar-beet crop of 1914 being the first to come 
on plats that had been in alfalfa. The normal course of the rotation 
was not in effect in these cases until 1915. In the other rotations 
the first alfalfa effect reached the beet crop only in 1915, and the full 
effect of three years of alfalfa was not obtained until the crop of 1917. 

Coming, as it does, in the second or third year after the alfalfa, the 
sugar-beet crop can not be expected to show the benefits of alfalfa 
in the rotation that are shown by the potatoes and oats. Yet in 
the 14 comparisons of mean yields shown in Table IV, 5 of the 
means show significant differences in favor of the alfalfa rotations; 
1 shows a significant difference against alfalfa, and 8 show differences 
that are not significant. 

If we consider only the comparisons in which the full course of 
alfalfa has been in effect, i. e., the yields for 1917 and 1918 for the 
6-year rotations, we have 40 annual comparisons, of which 24 show 
increased yields of 1 ton or more for the beets following alfalfa, while 
8 show decreases of 1 ton or more, and 8 show differences of less 
than 1 ton per acre. 



10 



BULLETIN" 881, U. S. DEPARTMENT OF AGRICULTURE. 



Table IV. — Effect of alfalfa on the yields of sugar beets at the Scottsbluff, Belle Fourche; 
and Huntley Field Stations, 1914 to 1918, inclusive. 



Station and rotation No. 




Yield of sugar 


oeets per acre (tons). 


1914 


1915 


1916 


1917 


1918 


Means. 


Scottsbluff: 


14.5 
21.2 


10.6 
16.3 


5.8 
10.4 


13.0 
17.7 


15.3 
21.8 


11.8+1.2 
17.5 + 1.4 








+6.7 


+ 5.7 


+4.6 


+4.7 


+ 6.5 


+ 5.7± .3 






22 (no alfalfa) 


14.2 
20.7 


12.0 
16.3 


7.3 
7.3 


11.1 
14.5 


14.3 
21.9 


11.8+ .7 




16.1 + 1.8 








+6.5 


+4.3 





+ 3.4 


+ 7.6 


+4.3+ .9 






30 (no alfalfa) : 




10.2 
12.5 


9.8 
7.3 


9.1 
15.3 


10.6 
16.0 


9.9± .2 






12.8 + 1.4 












+2.3 


-2.5 


+6.2 


+ 5.4 


+ 2.9±1.4 








31 (no alfalfa) 




15.6 
15.3 


17.1 
11.9 


16.0 
19.5 


20.2 
23.3 


17.2+ .7 






17.5±1.9 












-.3 


-5.2 


+3.5 


+3.1 


+ .3+1.4 








32 (no alfalfa) 




10.1 
13.3 


8.8 
6.8 


10.8 
15.4 


8.9 
16.5 


9.6+ .4 


62 (following alfalfa) 3d year 




13. Oil. 5 












+3.2 


-2.0 


+4.6 


+ 7.6 


+3.4+1.3 








Belle Fourche: 

20 (no alfalfa) . 


11.3 
12.8 


12.2 
11.0 


9.7 

8.8 


15.3 
14.1 


10.9 
11.0 


11.9+ .6 


40 (following alfalfa) 2d year 


11.5+ .6 








+1.5 


-1.2 


-.9 


-1.2 


+ .1 


— .4+ .4 






22 (no alfalfa) 


12.3 
11.1 


9.1 

7.0 


8.1 
4.2 


12.7 
10.0 


8.6 
8.9 


10.2+ .8 




8.2± .9 








-1.2 


-2.1 


-3.9 


-2.7 


+ .3 


-2.0+ .5 






30 (no alfalfa) . 




7.3 
9.4 


4.6 

7.2 


7.4 

12.7 


7.3 
13.7 


6.6+ .5 






10.7+1.2 












+2.1 


+2.6 


+ 5.3 


+6.4 

12.2 
13.8 


+4.1+ .9 








31 (no alfalfa) 




13.2 
10.9 


8.2 
10.4 


15.3 
15.7 


12.2 + 1.0 






12.7+1.0 












-2.3 


+2.2 


+ .4 


+ 1.6 


+ .5+ .7 








32 (no alfalfa) . . *. '. 




6.8 
8.3 


4.0 

4.8 


7.6 

8.5 


6.0 
9.9 


6.1+ .7 


62 (following alfalfa) 3d year 




7.9+ .7 












+ 1.5 


+ .8 


+ .9 


+3.9 


+ 1.8+ .5 








Huntley: 

20 (no alfalfa) 


15.1 
13.9 


8.3 
15.4 


15.3 
10.4 


9.6 
8.4 


14.6 
16.2 


12.6 + 1.2 




12.9+1.2 








-1.2 


+7.1 


-4.9 


-1.2 


+ 1.6 


+ .3 + 1.4 






22 (no alfalfa) 


10.4 
9.3 


6.8 
7.6 


11.1 
11.4 


11.3 
5.9 


10.2 
13.1 


10.0+ .5 




9.5+ .9 








-1.1 


+ .8 


+ .3 


-5.4 


+2.9 


-.5+ .9 






30 (no alfalfa) 




4.8 
12.9 


6.7 
7.4 


6.7 
8.3 


8.4 
14.2 


6.7+ .4 






10.7+1.6 












+8.1 


+ .7 


+ 1.6 


+ 5.8 


+4.0+1.4 








31 (no alfalfa) 




9.1 

8.7 


10.0 
15.6 


9.6 
13.0 


10.6 
14.7 


9.8+ .2 






13.0+1.0 












-.4 


+ 5.6 


+3.4 


+4.1 


+3.2+ .9 









In addition to recording the yield of beets from these rotation 
plats, it has been customary also to determine the average size of 
the beets by counting and weighing the product of several represent- 



EFFECT OF ALFALFA ON YIELDS OF FIELD CROPS. 11 

ative rows, to record the percentage of sugar in the beets as reported 
by the local sugar factory upon the samples from each plat, and to 
determine the proportion of the weight of the tops to the combined 
weight of beets and tops. This last determination is important not 
only as showing something of the vigor of growth of the sugar beets, 
but also as indicating the quantity of feed available as a by-product 
of the beet crop. 

The facts for each of the three stations regarding the effect of 
alfalfa in stimulating the yield of subsequent crops of sugar beets, as 
shown in Table IV, and also as to its effect on the size of beets, the 
percentage of sugar in the beets, and the percentage of tops are sum- 
marized below. 

At Scottsbluff the yield of beets from the 44 plat years averaged 
13.8 tons per acre, while the mean annual difference in favor of 
those following alfalfa (second and third year) was 3.4 ±0.5. The 
size of beets from the same plats averaged 1.53 pounds, with a mean 
annual difference in favor of those following alfalfa of 0.39 ±0.032. 
The sugar content of the beets for the 44 plat years averaged 17 per 
cent, with a mean annual difference against the plats following 
alfalfa of 0.5 ±0.15. The proportion of the weight of tops to the 
combined weight of beets and tops for the 44 plat years is 27 per 
cent, with a mean annual difference in favor of the beets following 
alfalfa of 2.3 ±0.6. 

At Belle Fourche the yield of beets for the 44 plat years averaged 
9.9 tons per acre, with a mean annual difference in favor of the plats 
following alfalfa (second and .third year) of 0.64 ±0.36. The size of 
the beets from the same plats averaged 0.78 pound, with a mean 
annual difference in favor of the plats following alfalfa of 0.08 ±0.035. 
The percentage of sugar in the beets averaged 19.7 per cent, while 
the mean annual difference in favor of the plats following alfalfa is 
0.5 ±0.19. The records as to percentage of tops are incomplete. 

At Huntley the yield of beets for, the 36 plat years averaged 10.7 
tons per acre, with a mean annual difference in favor of the plats 
following alfalfa of 1.5 ±0.6. The size of beets from the same plats 
averaged 0.96 pounds, with a mean annual difference in favor of those 
following alfalfa of 0.1 7 ±0.05. The sugar in the beets averaged 17 
per cent, with a mean annual difference against the plats following 
alfalfa of 1.3 ±0.22. The proportion of the weight of tops to the 
combined weight of beets and tops, omitting 1918, when the records 
were not made, has averaged 38 per cent, with a mean annual dif- 
ference in favor of the plats following alfalfa of 8 ±1.8. 

It is possible to make a comparison between the effect of alfalfa 
on the subsequent yield of beets and the effect of the application of 
farm manure at the rate of 12 tons per acre, as was done with the 
potato crop. The chief difference in the two comparisons is that 



12 



BULLETIN 881, U. S. DEPARTMENT- OF AGKICULTURE. 



where manure was used it was applied directly preceding the beet 
crop in three of the four cases, while in the alfalfa rotations one or 
two other crops occur between the alfalfa and the beet crops. There 
were four rotation pairs in the manure experiments previously de- 
scribed, 1 covering a 6-year period, 1912 to 1917. A summary of 
those results, together with the results given in the preceding para- 
graphs, is presented in Table V. These comparisons show that the 
period of alfalfa in the rotation has been nearly as beneficial as the 
periodical applications of farm manure, even though the position of 
the beet crop in the alfalfa rotations has not been so favorable as in 
the manured rotations. It is also to be remarked that while both 
manure and alfalfa have increased the yield of the beets, the size of 
beets, and the vigor of growth, as expressed in the larger proportion 
of tops, there has not been a corresponding increase in the per- 
centage of sugar in the beets. 

Table V. — Comparison of the effect of farm manure and of alfalfa on subsequent yields 
of sugar beets in irrigated-crop rotations at the Scottsbluff, Belle Fourche, and Huntley 
Field Stations. 



Factors compared. 



Mean yields per acre. 



Scottsbluff. 



Manure. Alfalfa 



Belle Fourche. 



Manure. Alfalfa 



Huntley. 



Manure. Alfalfa 



Yield of treated and untreated 

plats tons. 

Annual difference do... 

Size of beets pounds. 

Annual difference in size. do. . . 

Sugar in beets per cent . 

Annual difference do... 

Yield of tops do... 

Annual difference 



15.3 

+4.3±.28 
1.55 
+ .32±.044 

16.5 
-. 12±.20 

26 
+ 2.7±.6 



13.8 
+3.4±.5 
1.53 
+ .39±.032 

17.0 
+ .5±.15 

27 
+2.3±.6 



10.7 
+ 1.9±.36 
.84 
+.08±.035 

19.6 
4- .3±.22 



9.9 

+.64±!36 
.78 
+.08±.035 

19.7 
+ .5±.19 



11.3 
+2.6±.33 
. 92 
+ .21±!o34 

16.8 
+.16±.17 

32 
+ 3.2±1.12 



10.7 
+ 1.5±.6 
.96 
+ .17±.05 
17.0 
-1.3±.22 

38 
+ 8. Oil. 8 



SUMMARY. 

The effect of a period of two or three years of alfalfa in a rotation 
on the subsequent yields of Irish potatoes, oats, and sugar beets 
grown under irrigation has been tested for six years at three different 
stations in the northern Great Plains. Comparison is made between 
the yields of these crops when grown in the same sequence but with- 
out alfalfa. A further comparison is made in the case of potatoes 
and sugar beets as to the relative effect of a period of alfalfa in the 
rotation and the application of farm manure at the rate of 12 tons 
per acre once during the period of the rotation. 

At Scottsbluff, Nebr., where the soil is light sandy loam, the effect 
of alfalfa has been to increase the yield of potatoes about 100 bushels 
per acre, to increase the proportion of marketable potatoes about 12 
per cent, to increase the yield of oats about 6 bushels per acre, and 
to increase the yield of sugar beets 3.4 tons per acre. 



i Scofield, C S. Loc. cit. 



EFFECT OF ALFALFA ON YIELDS OF FIELD CROPS. 13 

At Belle Fourche, S. Dak., where the soil is heavy clay loam rich 
in organic matter, there has been no beneficial effect from alfalfa on 
the subsequent potato crop, and the effect on oats and sugar beets, 
while apparently beneficial, has been too slight to be regarded as 
significant. 

At Huntley, Mont., on a very productive clay-loam soil, the effect 
of alfalfa has been to increase the yield of potatoes about 50 bushels 
per acre, without, however, increasing the proportion of marketable 
potatoes, which has been relatively high on all plats. The alfalfa 
has apparently increased the yield of oats about 1 1 bushels per acre 
and the yield of sugar beets about 1.5 tons per acre. 

A comparison of the results from the use of alfalfa in the rotation 
with those from the use of farm manure shows that with potatoes at 
Scottsbluff the alfalfa is distinctly more beneficial than farm manure, 
although the latter gives excellent returns. With the other crops 
and at the other stations the differences between the effects are less 
striking, and in general the farm manure has given better results. 



WASHINGTON : GOVERNMENT PRINTING okeige : 1920 



LIBRARY OF CONGRESS 



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